1. Field of the Invention
The present invention relates to an information recording/reading head for recording information in an information recording medium by using a small probe or for reading information recorded in the information recording medium.
2. Description of the Related Art
In general, an optical disk apparatus, a magneto-optical disk apparatus, a Hard Disk Drive (HDD) apparatus, or the like are widely used as a high-density, large-capacity recording/reproducing apparatus. In the beginning, even these recording/reproducing apparatuses were expected to satisfy a requirement for using temporal information because it realized large capacity recording which greatly exceeded the recording capacity of a conventional recording/reproducing apparatus. However, growing the requirement for using information is unending, and a recording/reproducing apparatus which allows the high density, large capacity recording is eagerly desired to be developed.
In general, in a magnetic recording medium, the deterioration of recording bits, which is caused by thermal fluctuation, prevents the improvement of a recording density. On the other hand, in an optical recording medium, the diffraction limit of light draws an upper limit of the recording density. Therefore, in order to try to improve the recording density, one needs to overcome such limits; however, this is not easy.
Under these circumstances, a recording/reproducing apparatus using a Scanning Probe Microscope (SPM) method is under development as a technique which can realize the high density, large capacity recording. According to this recording/reproducing apparatus, it is theoretically possible to realize super high density recording, which exceeds 1 tera bit per 6.45 square centimeters (i.e. 1 square inch).
For example, a recording/reproducing apparatus using a Scanning Nonlinear Dielectric Microscopy (SNDM) method has a probe having a tip portion with a radius on the nanometer order, and it uses a ferroelectric material as a recording medium. Information is recorded by applying an electric field, which is stronger than a coercive electric field of the ferroelectric material, from the probe to the ferroelectric material and by forming polarization domains having predetermined polarization directions in the ferroelectric material. Moreover, the information is reproduced by detecting the polarization state of the ferroelectric material on the basis of frequency change of an oscillation signal, which oscillates at a resonance frequency of a resonance circuit formed from a capacitance of the ferroelectric material just under the probe and from an inductor.
Furthermore, there is also developed a SPM recording/reproducing apparatus which has a cantilever having a nonoscale tip portion and which uses a polymer film as a recording medium. In such an apparatus, information is recorded by heating the tip portion of the cantilever to put a small mark on the polymer film by the heat.
However, in the recording/reproducing apparatus using SPM or SNDM, dusts may be attached to the probe in some cases because the probe with a radius on the nanometer order is exposed in the vicinity of a recording surface of the recording medium. Of course, dusts from the outside may possibly be prevented by putting a recording/reproducing mechanism, which includes the probe and the recording medium, in a sealed case. Even inside the sealed case, however, dusts may be made by the abrasion of driving portions of the recording medium and the recording/reproducing mechanism, so that it is difficult to prevent such dusts from attaching to the probe.
The recording/reproducing apparatus using the SNDM detects the polarization state (i.e., a dielectric constant) of the ferroelectric material in order to reproduce information recorded in the ferroelectric material. The polarization state can be detected by measuring the capacitance of the ferroelectric material located just under the tip portion of the probe. In order to detect this capacitance, it is required to bring the tip portion of the probe into contact with the surface of the ferroelectric material or to position the tip portion of the probe near the surface of the ferroelectric material. Therefore, if dusts attach to the probe, the capacitance is changed by the dusts, and information reproduction accuracy decreases. Moreover, even when an electric field is applied to the ferroelectric material to record information, a distribution of the electric field to be applied changes in some cases if dusts attach to the probe. As a result, the electric field is not surely applied, and information recording accuracy decreases.
Moreover, the decrease in the accuracy of recording and reproducing may occur in the same manner, even in the recording/reproducing apparatus of a system for applying heat to a polymer film with a cantilever to record a mark.
Furthermore, in the recording/reproducing apparatus using the SPM or SNDM, the recording medium, such as a plate-shaped or disc-shaped medium, is moved parallel to its recording surface with the probe fixed. There is also the apparatus in which the probe is moved with the recording medium fixed. The probe has a radius on the nanometer order and is extremely thin. Therefore, if the probe or the recording medium is moved with dusts existing between the probe and the recording surface of the recording medium, an external force is applied to the probe, so that the probe may be destroyed. Moreover, it is also conceivable that dusts collide with the probe in motion, thereby misaligning and destroying the probe. As a result, a recording/reading head may break down, or the durability thereof cannot be improved.